Two-stage tie-down of turbomachine rotor

ABSTRACT

A turbomachine rotor comprises a compressor assembly of prebalanced bladed hubs telescoped over a central shaft. The hubs are held against an end flange by a suitable retaining nut with a first predetermined axial preload and then statically and dynamically balanced as a unit. A compressor turbine hub is prebalanced and then telescoped over the central shaft. The turbine hub is secured against the aft face of the compressor hub by an additional retaining nut with a second predetermined preload. The entire assembly may then be statically and dynamically balanced. The axial preloads are selected so that the compressor hubs are held with sufficient axial force in the final assembly. This type of construction permits the turbine hub to be removed from the shaft for replacement or repair without disturbing the balance of the compressor assembly.

1 Oct. 21, 1975 United States Patent 1191 Strani TWO-STAGE TIE-DOWN OF Primary ExaminerEverette A. Powell, Jr.

TURBOMACHINE ROTOR Attorney, Agent, or Firm-Charles M. Hogan; Irwin P.

Garfinkle [75] Inventor.

Salvatore Stranm, Orange, Conn. g y M. Gm

[73] Assignee:

[22] Filed:

[57] ABSTRACT A turbomachine rotor comprises a compressor assembly of prebalanced bladed hubs telescoped over a central shaft. The hubs are held against an end flange by a suitable retaining nut with a first predetermined axial preload and then statically and dynamically balanced as a unit. A compressor turbine hub is prebalanced and then telescoped over the central shaft. The

46 9 4mA9 m w 4m BFMW 0 1 W N H 1 4 W "4 "4 .H2 "m "61 "m4 mmh .e .H... Una .8 US L .f. C rm t e Umm II] 2 555 [ll turbine hub is secured against the aft face of the com- [56] References Cited pressor hub by an additional retaining nut with a sec- UNITED STATES PATENTS- ond predetermined preload. The entire assembly may 1 221 087 4/1917 Parsons et 416/244 A be statically and dynamically balanced- The axial 2:749:086 6/1956 Lombard 416/201 preloadS are Selected SO that the Compressor hubs are 2,928,649 3/1960 Lombard et al. 416/l98 A held with u f c e t axial force in the final assembly.

2,988,324 6/1961 Sutters................................ 416/201 This type of construction permits the turbine hub to FOREIGN PATENTS OR APPLICATIONS be removed from the shaft for replacement or repair without disturbing the balance of the compressor assembly.

496,948 4/1930 Germany 416/199 158,6Il 4/1957 Sweden........................... 416/198 A 2 Claims, 1 Drawing Figure US. Patent Oct. 21, 1975 3,914,070

TWO-STAGE TIE-DOWN OF TURBOMACHINE ROTOR The present invention relates to turbomachines and more specifically to rotor assemblies for this type of machine.

The rotating components of a gas turbine engine are referred to generally as a rotor assembly. It will consist of bladed hubs positioned end to end for rotation about a common axis. In the past it has been common practice to stack these hubs over a central shaft and sandwich them in this position by a nut threaded on one or both ends of the shaft (see US. Pat. No. 2,530,477). The stacked discs are balanced as an entire assembly for rotation about the axis of the central shaft. While this type of rotor construction secures the hubs in a highly effective and simplified fashion, it presents certain problems. One of the problems arises when one 'or more of the hubs needs to be replaced. When it is necessary to remove one of the hubs the balance of the rotor is upset and the entire unit must be rebalanced. This laborious and time-consuming process greatly adds to maintenance costs for an engine incorporating this type of rotor.

in accordance with the present invention the above problems are solved by assembling one or more bladed hubs (preferably prebalanced) on a central shaft with a first given axial preload and balancing this assembly. A second prebalanced bladed hub is placed on the shaft and held against the hub assembly with asecond axial preload. The entire unit is balanced as an assembly. The level of the axial preloads is selected so that the preload holding the second hub in place will assure retention of the desired axial preload for the first hub or hubs.

The above and other related objects and features of the present invention will be apparent from a reading of the following description of the disclosure shown in the accompanying drawing and the novelty thereof pointed out in the appended claims.

The single FIGURE shows a simplified, longitudinal section view of a gas turbine engine incorporating a rotor assembly which embodies the present invention.

Referring to the figure, there is shown a gas turbine engine comprising an output gearbox l and an annular inlet housing 12 secured to the gearbox which defines an annular inlet 14 to a compressor assembly, indicated at 16. Compressor 16 has bladed rotor elements, to be described later, which pressurize air for delivery through a diffuser 18 into a chamber defined by outer housing 20 and an aft cast strut assembly 22. A perforated combustor 24 is positioned within this pressure chamber and has fuel nozzles 26 for the injection of fuel to be mixed with pressurized air in combustor 24. A suitable device ignites the mixture to produce a hot gas stream which is discharged through a turbine inlet duct 28 and a turbine inlet nozzle 30 and across a turbine assembly 32 comprisingrotor elements to be described later. From there the hot gas stream passes by struts 34 and across a bladed power turbine rotor 36 for discharge to the atmosphere. Power turbine rotor 36 is connected to an output shaft 38 extending forward to a gear set (not shown) in the gearbox 10 to provide a rotary power output.

The compressor 16 and turbine assembly 32 comprisea bladed hub 40 defining an axial stage and a bladed hub 42 comprising a centrifugal stage. Hubs 40 and 42 are annular inform and are telescoped over a shaft 44 which is journaled forv rotation at its forward end by bearingassembly 46, secured to inlet housing 12. Hub 40has an integral forward conical extension 48 which abuts an integral flange 50 on shaft 44. A retaining nut 52 is threaded over external threads 54 on shaft 44 to hold hubs 40 and 42 against flange 50 with a'first predetermined axial preload, to be described later. I

The turbine assembly 32 comprisesa bladed hub 56 defining an axial stage. Hub 56 is annular in form and telescoped over the aft end of shaft 44. A conical annular spacer element 58 abuts a shoulder 60 on the aft face of hub 42 and another shoulder 62 on the forward face of hub 56. A bearing assembly 63 journals the aft end ofshaft 44 in the strut assembly 34. A retaining nut 65 is threaded over an external threaded section 64 in the aft end of shaft 44 to secure the hub 56 against the aft face of hub 42 with a second predetermined axial preload to be described later. It should be apparent that the axial preload passes through the inner race of bearing assembly 63 and suitable spacer elements between the nut 65 and the hub 56.

Assembly of the rotor for the engine takes place as follows: Hubs 40 and 42 are individually prebalanced. They are then telescoped over shaft 44 and secured against flange 50 by nut 52 with the first given axial preload. This subassembly then is statically and dynamically balanced for rotation about the axis of the shaft 44 using suitable balance units. Generally, balancing will be achieved by removing material from the hubs 40 and 42. The turbine hub 56 is suitably statically and dynamically balanced for rotation about its central axis as a unit. It then is telescoped over shaft 44 with conical spacer 58 and held against the aft face of hub 42 by the nut 65 with the second predetermined preload. The entire assembly is then statically and dynamically balanced for rotation about the central axis. Balancing of the entire unit is achieved by removing material only from the turbine hub 56 or the spacer 58 so as not to upset the balance of the compressor rotor subassembly. The complete balanced rotor is then assembled into the engine for normal operation.

The first and second axial preloads are selected so that the second axial preload imposed by nut 65 does not counteract the preload imposed by nut 52. Generally speaking, this means that the preload imposed by nut 52 should be higher than that for nut 65 so that the net assembled preload for nut 52 is still a positive amount sufficient to hold the hubs 40 and 42 in place.

As operating time accumulates on the engine, it may be necessary to remove the turbine 32, since it operates at a much higher temperature than that for the compressor assembly 16. To replace or repair this unit it is simply necessary to remove nut 65 and disassemble hub 56 from shaft 44. Since nut 52 holds the hubs 40 and 42 in place and this connection is not disturbed, the balance of the compressor rotor subassembly remains intact. To replace the turbine with a new one it is simply necessary to balance the new turbine hub 56 and place it on the shaft for final balancing.

The above arrangement greatly simplifies and minimizes the cost for engine maintenance. it greatly facilitates replacement of the turbine which is a part that needs fairly frequent replacement or inspection. While the preferred embodiment of the present invention has been described, it should be apparent to those skilled in the art that it can be employed in different forms without departing from its spirit and scope.

Having described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

l. A turbomachine rotor comprising:

a central shaft;

a first bladed hub means having a central opening and telescoped over said shaft, said first bladed hub means comprising a single axial stage and a downstream centrifugal impeller abutting one another;

means for releasably securing said first hub means on said shaft with a first predetermined axial preload, said first means comprising a flange adjacent one end of said shaft and a threaded element axially holding said first hub means against said flange;

a second bladed hub means having a central opening and telescoped over said shaft adjacent said first hub means, said second hub means comprising a mined axial preloads preventing loosening of said first hub means when the second releasable securing means tightens said second hub means on said shaft.

2.. A turbomachine rotor as in claim 1 wherein said turbine is spaced from said compressor and said rotor further comprises an annular spacer element abutting an end face of the centrifugal impeller and an end face of the turbine. 

1. A turbomachine rotor comprising: a central shaft; a first bladed hub means having a central opening and telescoped over said shaft, said first bladed hub means comprising a single axial stage and a downstream centrifugal impeller abutting one another; means for releasably securing said first hub means on said shaft with a first predetermined axial preload, said first means comprising a flange adjacent one end of said shaft and a threaded element axially holding said first hub means against said flange; a second bladed hub means having a central opening and telescoped over said shaft adjacent said first hub means, said second hub means comprising a single stage axial flow turbine; and a second means for releasably securing said second hub means on said shaft against said first hub means with a second predetermined axial preload, said second means comprising a threaded element axially holding said second hub means against said first hub means, said first threaded element asserting a greater axial preload than said second threaded element, said first and second predetermined axial preloads preventing loosening of said first hub means when the second releasable securing means tightens said second hub means on said shaft.
 2. A turbomachine rotor as in claim 1 wherein said turbine is spaced from said compressor and said rotor further comprises an annular spacer element abutting an end face of the centrifugal impeller and an end face of the turbine. 